1. Field of the Invention
The invention relates to a condensation heat exchanger intended to equip a gas boiler for domestic application.
2. Background Information
This exchanger is particularly intended to equip a gas boiler for domestic applications, in order to supply a central heating circuit and/or to provide water for sanitary use.
The subject heat exchanger of the invention, more precisely, is a double exchanger constituted by a primary exchanger directly exposed to hot gases generated by the gas burner, and by a secondary exchanger which is exposed to the gases, of considerably lower temperature, which escape from the primary exchanger.
The water, or any other fluid to be heated, circulates in this double exchanger, counter-current to the fumes, that is, by passing first through the secondary exchanger, where it undergoes preheating, then into the primary exchanger where it undergoes heating, properly speaking.
By way of indication, the burnt gases coming directly out of the burner are at a temperature of the order of 1000° C.
After passing through the primary exchanger, their temperature is generally between 100 and 180° C.
These hot gases contain a certain quantity of water as vapour which may condense when it comes into contact with the wall of the secondary exchanger, while it is below the dew point, of the order of 60° C.
This condensation provides supplementary calories to the water circulating in the secondary exchanger, these calories corresponding to the latent heat of evaporation.
A double exchanger of this type, which is described for example in the document EP 0 078 207, enables the yield of the apparatus to be substantially improved.
In the document WO 94/16272 a heat exchanger element is described which consists of a tube of thermally well conducting material in which a coolant fluid, for example water to be heated, is intended to circulate.
This tube is wound in a helix and has a flattened and oval cross section with the major axis substantially perpendicular to the axis of the helix, and each turn of the tube has flat faces which are separated from the faces of the adjacent turn by an interstice of constant height, this height being substantially smaller than the thickness of the said cross section, the spacing between two adjacent turns being furthermore sized by means of cross members which are constituted by bosses formed in the wall of the tube.
This document also describes heat exchangers having several elements such as the above, which are formed in different ways in the various described embodiments.
An exchanger element, so designed, ensures a very large heat exchange between the hot gases passing close to the tubular element and the fluid to be heated which circulates within it.
In fact, during its passage through the interstice between the turns, the flow of hot gases is in contact with a relatively extended surface of the wall of the exchanger element.
The present invention more particularly has as its subject to propose a condensation heat exchanger of the general type mentioned above, the heat exchange elements of which are bundles of flat tubes such as those known from WO 94/16272, which may be consulted if need be.
The prior art closest to the subject of the present invention corresponds to the embodiment illustrated in FIG. 22 of the above document.
The apparatus in question is composed of two parallel bundles of tubes, a primary one referenced 1 and a secondary one referenced 1′.
These two bundles are disposed close to one another, with their axes parallel, and are fixedly mounted within an envelope 8 (termed “body” in the document).
The hot gases are provided by an external apparatus 9 and penetrate via a duct 90 and a cuff 80 into the central portion of the principal exchanger 1 (arrows J0). The hot gases pass radially through the latter, from the inside to the outside (arrows J1), then pass through the secondary exchanger, always radially, but this time from the outside to the inside (arrows J2).
Finally, the cooled gases leave this double exchanger by a cuff 81 (arrows J3).
The object of the invention is to improve the apparatus very schematically shown in FIG. 22 of WO 94/16272, to increase the compactness.
In fact, a constraint often encountered by installers of this kind of apparatus is related to the space available to receive it, which is often reduced.
The invention also has as its object to propose a relatively light apparatus, so as to make the operations of transport, positioning, and fixing in place by the installer more convenient.
The invention springs from the inventor's observation that the energy to be recovered in the secondary exchanger is always smaller than that which is captured by the primary exchanger.
Starting from this observation, it can be deduced that the heat exchange surface of the secondary exchanger, which is proportional to the length of the tube bundle, may be reduced with respect to that of the primary exchanger.
In this way, if the axial dimension of the secondary bundle is reduced, an available space is formed at one of its ends, and may be made use of to install there the evacuation cuff of the burnt, cooled gases.
The bulk of this cuff in the axial direction is therefore not added to that of the apparatus proper, in contrast to the known embodiment of FIG. 22 of WO 94/16272; it fits within that of the apparatus.
Furthermore, the tube length of the secondary exchanger being reduced, the apparatus is of course lighter than an apparatus with primary and secondary coils of the same length, as in the cited apparatus.
Finally, always with the aim of improving compactness, use is made, according to the invention, of a cylindrical burner which is mounted within the primary bundle.
In this way, the axial dimension of the burner is also inscribed within the axial dimension of the envelope.
The subject of the invention is consequently a condensation heat exchanger associated with a gas or fuel oil burner which is composed of two parallel tube bundles disposed adjacent to one another and fixedly mounted within an envelope impermeable to the gases, these two bundles communicating one to another via a “transfer” collector, means being provided for circulating a fluid to be heated, in particular cold water, firstly within tube(s) constituting the secondary bundle, then—via the said transfer collector—within the tube(s) constituting the said primary bundle, the said envelope surrounding the two tube bundles, while being closely spaced apart, this envelope having an exhaust sleeve for the combusted gases which is positioned in the neighbourhood of the said secondary bundle, this exchanger being constructed so that the hot gases generated by the burner pass radially, or approximately radially, passing through the interstices separating the turns, firstly the said primary bundle, then the secondary bundle, and are then evacuated out of the exchanger through the said sleeve.